Pre-treatment process for electroless nickel plating

Abstract

The present invention discloses a process for electroless plating of nickel onto copper features of a printed circuit board which suppresses extraneous nickel plating. The process comprises the steps i) activation of the copper features with palladium ions; ii) removal of excessive palladium ions or precipitates formed thereof with a pre-treatment composition comprising at least two different types of acids wherein one type is an organic amino carboxylic acid and iii) electroless plating of nickel.

1 . A process for deposition of electroless nickel which suppresses extraneous nickel plating on a substrate having a copper patterned surface after activation with an ionic palladium activator comprising the following steps:
 i. contacting a substrate containing a copper surface with a palladium ion containing composition; thereafter   ii. contacting the copper containing surface with a composition comprising an organic amino carboxylic acid to rinse off palladium ions and precipitates formed thereof; represented by formula 1 or formula 2 or a mixture of formula 1 and formula 2:   
       
         
           
           
               
               
           
         
         
           wherein R11, R12, R21 and R22 are independently selected from the group consisting of H, C 1 -C 4  alkyl, linear or branched; R31, R32, R33, R34 and R35 are independently selected from the group consisting of H, phenyl, benzyl, C 1 -C 4  alkyl, linear or branched, substituted or unsubstituted, wherein the substituents are selected from the group consisting of —OH, —SH, —NH 2 , —COOH; R41 and R42 are independently selected from the group consisting of H, C 1 -C 4  alkyl, linear or branched, or a counter ion selected from the group consisting of Na + , K + , NH 4   + ; and 
         
         iii. electroless plating of nickel onto said treated copper containing surface. 
       
     
     
         2 . The process according to  claim 1  wherein the pre-treatment composition in step ii. further comprises an acid selected from the group consisting of sulfuric acid, hydrochloric acid, toluene sulfonic acid, methane sulfonic acid, formic acid and acetic acid. 
     
     
         3 . The process according to  claim 2  wherein the concentration of the further acid ranges from 25 g/l to 150 g/l. 
     
     
         4 . The process according to  claim 1 , wherein the suitable counter ion is selected from the group consisting of Na + , K + , NH 4   + . 
     
     
         5 . The process according to  claim 1 , wherein R11, R12, R21 and R22 are selected independently from H, methyl and ethyl. 
     
     
         6 . The process according to  claim 1 , wherein R31, R32, R33, R34 and R35 are independently selected from the group consisting of H, methyl, ethyl, —CH 2 OH, —CH 2 NH 2 , —CH 2 COOH, —CH 2 CH 2 OH, —CH 2 CH 2 NH 2 , —CH 2 CH 2 COOH, —CH 2 SH, —CH 2 CH 2 SH and —CH 2 CONH 2 . 
     
     
         7 . The process according to  claim 1 , wherein the organic amino carboxylic acid is selected from the group consisting of alanine, asparagine, aspartic acid, cysteine, glutamic acid, glycine, isoleucine, leucine, lysine, serine, phenylalanine, methionine, threonine, valine, N,N-dimethyl glycine. 
     
     
         8 . The process according to  claim 1 , wherein the organic amino carboxylic acid is selected from the group consisting of β-alanine, β-leucine, β-isoleucine, β-glutamine, β-glutamic acid, β-methionine, 3-asparagic acid. 
     
     
         9 . The process according to  claim 1 , wherein the concentration of the at least one amino carboxylic acid ranges from 0.1 g/l to 100 g/l. 
     
     
         10 . The process according to any of the foregoing claims  claim 1 , wherein the copper surface is on a printed circuit board substrate. 
     
     
         11 . The process according to  claim 1 , wherein in Formula 1, R11, R12, R21 and R22 are selected independently from H, methyl and ethyl and in Formula 2, R31, R32, R33, R34 and R35 are independently selected from the group consisting of H, methyl, ethyl, —CH 2 OH, —CH 2 NH 2 , —CH 2 COOH, —CH 2 CH 2 OH, —CH 2 CH 2 NH 2 , —CH 2 CH 2 COOH, —CH 2 SH, —CH 2 CH 2 SH and —CH 2 CONH 2 . 
     
     
         12 . The process according to  claim 1 , wherein in Formula 2, R31, R32, R33, R34 and R35 are independently selected from the group consisting of H, methyl, ethyl, —CH 2 OH, —CH 2 NH 2 , —CH 2 COOH, —CH 2 CH 2 OH, —CH 2 CH 2 NH 2 , —CH 2 CH 2 COOH, —CH 2 SH, —CH 2 CH 2 SH and —CH 2 CONH 2  and in Formula 1, the organic amino carboxylic acid is selected from the group consisting of β-alanine, β-leucine, β-isoleucine, β-glutamine, β-glutamic acid, β-methionine, β-asparagic acid. 
     
     
         13 . The process according to  claim 1 , wherein in Formula 2, R31, R32, R33, R34 and R35 are independently selected from the group consisting of H, methyl, ethyl, —CH 2 OH, —CH 2 NH 2 , —CH 2 COOH, —CH 2 CH 2 OH, —CH 2 CH 2 NH 2 , —CH 2 CH 2 COOH, —CH 2 SH, —CH 2 CH 2 SH and —CH 2 CONH 2 , and in Formula 1, the organic amino carboxylic acid is selected from the group consisting of alanine, asparagine, aspartic acid, cysteine, glutamic acid, glycine, isoleucine, leucine, lysine, serine, phenylalanine, methionine, threonine, valine, N,N-dimethyl glycine.